1. Field of the Invention
The present invention concerns an initiation fixture and initiator assembly including the fixture. The initiator assembly facilitates the initiation of a signal in a non-electric fuse such as a signal-transmission tube, e.g., shock tube. The initiator assembly comprises a triggering device within which the initiation fixture is received. The triggering device initiates a signal within the fuse which signal serves to initiate a detonator or other signal-transmitting or explosive device connected to the remote end of the fuse.
2. Related Art
U.S. Pat. No. 5,365,851 to Shaw, issued Nov. 22, 1994 and entitled “Initiator Device”, discloses (see FIGS. 1 and 2) an initiation fixture (16) for an impulse transmission tube comprising a sleeve (30) in which a shock tube fuse (10) is received. A primer (percussion) cap (28) is contained at one end of sleeve (30) in signal-transfer proximity to the input end of the shock tube (10); the opposite (output) end of shock tube (10) has a detonator (14) secured thereto. An internal fence (32) establishes a touch hole (33) between the primer cap (28) and the input end of the shock tube (10). A threaded retainer means (40) is movably and rotatably disposed on the exterior surface of sleeve (30) to engage internal threads formed in the end of barrel (22) of a triggering device (18). A first stop means (42) positions retainer (40) to properly locate primer cap (28) for detonation by operation of a striking firing pin (20) of triggering device (18). An initiation fixture such as fixture (16) of Shaw U.S. Pat. No. 5,365,851 is usable only with a triggering device having the interior threads needed to accommodate the exterior threads on the body of the device.
Triggering devices for use in firing initiation fixtures such as those disclosed by the above-described Shaw U.S. Pat. No. 5,365,851 (“the Shaw patent”), are usually comprised of a barrel containing at one end a trigger-operated, spring-loaded firing pin and having, at the other (output) end of the barrel, means for connecting the initiation fixture to the barrel. Alternatively, the triggering device may contain a percussion cap and a structure for receiving and retaining the input end of a fuse in signal-transfer proximity to the percussion cap. In such case, the output end of the barrel of the triggering device usually contains a grommet or other tube-retaining structure within or aligned with an aperture formed in a fuse-holder cap fitted over the output end of the barrel. The input end of the fuse is simply inserted into the aperture and advanced until it encounters a stop member, at which point the fuse is positioned within the barrel in signal-transfer proximity to the initiation charge of the triggering device, provided only that the user has taken care to fully insert the fuse. Such triggering devices usually employ a safety mechanism and, once the safety mechanism is placed in the armed position, the trigger of the device is operated so that the firing pin strikes and initiates the initiation charge, thereby initiating a signal in the fuse. As illustrated in the Shaw patent, the other (output) end of the fuse may be connected to a detonator; obviously, it may be connected to any other device which is operated by the signal engendered in the fuse.
Whether an initiation fixture such as that of the Shaw patent is utilized, or whether the input end of the fuse is simply inserted into a triggering device containing its own initiation charge, assembly of the initiator to the triggering device or insertion of the exposed end of the fuse is required in the field at the point of use. Such field assembly or insertion may be difficult because of weather conditions or darkness, and exposes the necessarily open input end of the fuse and the interior of the triggering device to the elements, with potential adverse consequences on reliability of initiation.